The effectiveness of electromagnetic dent removers, that is, dent removers that use electromagnetic energy to remove dents from conductive materials, is well known in the prior art. These dent removers are commonly used in the aircraft manufacturing and repair industry as well as in other industries, such as in the automotive industry. One very common use of an electromagnetic dent remover is for the removal of dents from the outer "skin" of assembled aircraft or aircraft parts, such as wing assemblies. The outer skin is usually made of conductive sheet material that is fastened to an internal frame of the aircraft. Once the skin has been fastened to the frame, the inside surface of the skin is, many times, inaccessible. Electromagnetic dent removers are well suited to removing dents from the aircraft skin because they do not require access to the inside surface of the skin.
An electromagnetic dent remover uses an electric coil, commonly referred to as a work coil, to remove a dent. To remove a dent from a conductive part, such as the skin of an aircraft, the work coil is placed on the dented part and positioned over the dent. An electric current is applied to the work coil, which produces an electromagnetic field that penetrates the dented part. In a conventional manner, the electromagnetic field exerts a repelling force on the dented part. While the repelling force is quite strong, it typically is not strong enough to deform the dented part. By properly controlling the electric current applied to the work coil, the electromagnetic field is caused to rapidly collapse. The collapsing electromagnetic field causes the repelling force to reverse, thereby exerting a pulling force on the part. Unlike the repelling force, however, the pulling force is normally strong enough to deform the dented part. Thus, the pulling force is used to pull the dent from the part. An example of such a dent remover is described in U.S. Pat. No. 3,998,081, entitled "Electromagnetic Dent Puller". The disclosure of U.S. Pat. No. 3,998,081, and particularly the portion of the disclosure describing the production and application of electric current to the electromagnetic work coil, is incorporated herein by reference.
It is well known in the prior art that the electromagnetic field should be concentrated at the dent so that adjacent areas of the part will not be deformed when the dent is removed. One successful prior art approach concentrates the electromagnetic field by using a work coil having a stressing region whose shape and size are adapted to a particular dent configuration. The stressing region produces a concentrated electromagnetic field that is localized in the area of the dent. Several examples of work coils that produce localized electromagnetic fields are described in U.S. Pat. No. 4,061,007, entitled "Electromagnetid dent Remover with Electromagnetic Localized Work Coil", the disclosure of which is hereby incorporated by reference.
While electromagnetic dent removers of the type described in U.S. Pat. Nos. 3,998,081 and 4,061,007 have proven to be somewhat satisfactory, they are not as satisfactory as desirable. One problem with these prior art dent removers is that while they may be effective in removing dents from relatively rigid parts, they are substantially less effective in removing dents from flexible parts (or flexible portions of rigid parts). In a rigid part, the area around a dent is stabilized by the inherent rigidity of the part. As a result, the area adjacent the dent is minimally affected (if at all) by the forces exerted on the dent by the dent remover. The rigidity of the part permits the repelling force and the pulling force to be concentrated at the dent, which facilitates removal of the dent.
In flexible parts, such as the skin of an aircraft, flexibility of the skin actually hinders dent removal by the prior art dent removers. The skin, including the dent and the area adjacent to the dent may be temporarily flexed by the forces exerted on it by the dent remover. That is, the repelling force of the work coil may cause the skin to flex in the direction away from the work coil. When the pulling force is exerted on the part, the skin, including the dent and the area adjacent to the dent, is again flexed, this time in the direction of the work coil. This flexing of the skin causes the pulling force to be dissipated into the area of the part adjacent the dent. As a result, the strength of the pulling force exerted on the dent is reduced and the removal of the dent is made more difficult.
One approach used with the prior art dent removers to overcome the problem of removing dents in flexible parts, is to increase the pulling force exerted on the part. However, increasing the pulling force requires that the electromagnetic field that exerts the repelling force be increased, which causes further flexing of the part away from the work coil. Thus, some of the increased pulling force is dissipated into the area surrounding the dent when the part is flexed toward the work coil, thereby reducing the pulling force exerted on the dent.
Another approach used by the prior art dent removers is to mechanically stabilize the part by placing weights, such as sand bags, around the dent. The weights essentially "preflex" the part, so that it is not flexed away from the work coil by the repelling force of the work coil. Further, the weights prevent the part from being flexed toward the work coil by the pulling force. Thus, mechanically stabilizing the part in this way allows the pulling force to be concentrated at the dent. Unfortunately, this approach, while somewhat effective, is not very accurate. Shifting of the weights, or improper placement of the weights may allow some flexing of the part. Further, the labor associated with placement of the weights is rather costly. In some instances, the mere weight of the dent remover is sufficient to stabilize a flexible part. However, the weight of the dent remover may be overcome by the repelling pulling forces exerted by the work coil when very strong pulling forces are necessary to remove a dent.
As can be readily appreciated from the foregoing discussion, there is a need for an electromagnetic dent remover that is effective in removing dents from flexible parts or flexible areas of rigid parts. This invention is directed to a dent remover with a tapped work coil that exerts a stabilizing force concurrently with a pulling force to achieve these results.